manuzhang commented on code in PR #3071:
URL: https://github.com/apache/iceberg-rust/pull/3071#discussion_r4338226244
##########
crates/catalog/sql/src/catalog.rs:
##########
@@ -338,22 +339,32 @@ pub enum SchemaVersion {
impl SchemaVersion {
/// Detect the schema version of an existing catalog table by
introspecting its columns.
async fn detect(pool: &AnyPool) -> Result<Self> {
- let catalog_table_description = pool
- .describe(&format!("SELECT * FROM {CATALOG_TABLE_NAME}"))
- .await
- .map_err(from_sqlx_error)?;
-
- let has_type_column =
catalog_table_description.columns().iter().any(|column| {
+ Self::probe(pool).await.map_err(from_sqlx_error)
+ }
+
+ async fn probe(pool: &AnyPool) -> sqlx::Result<Self> {
+ let mut transaction = pool.begin().await?;
+ // Run both reads as one unprepared batch in a transaction. The empty
read refreshes
+ // the schema before the second statement prepares its column
metadata. The second
+ // statement returns one NULL row even for an empty catalog.
+ let probe = format!(
+ "SELECT * FROM {CATALOG_TABLE_NAME} WHERE 1 = 0; \
+ SELECT catalog.* FROM (SELECT 1) AS probe \
+ LEFT JOIN {CATALOG_TABLE_NAME} AS catalog ON 1 = 0"
+ );
+ let catalog_row = transaction
+ .fetch_all(sqlx::raw_sql(&probe))
+ .await?
+ .pop()
+ .ok_or(sqlx::Error::RowNotFound)?;
Review Comment:
I'm hesitating to add MySQL or Postgres in unit tests. @blackmwk WDYT?
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